Flexible hose

ABSTRACT

A flexible hose ( 1 ) with a corrugated wall ( 2 ), comprising an internal surface ( 3 ) with projections ( 4, 5 ) and recesses ( 6, 7 ), said hose ( 1 ) being obtained by moulding a plastic material, wherein each internal projection ( 4, 5 ) comprises a substantially flat and smooth top face ( 8, 9 ). Each top face ( 8, 9 ) has a first width (W 1 ) and each internal recess has a second width (W 2 ). The ratio between first width and second width (W 1 /W 2 ) is preferably larger than or equal to 2.2. The hose may comprise a hollow longitudinal protuberance or score.

This invention relates to a flexible corrugated hose according to thepreamble of the first claim.

Such flexible corrugated hoses find numerous applications, for instancein vacuum cleaners and other industrial applications. This and othertypes of hoses are often produced by blow-moulding a thermoplasticmaterial, as this provides lightweight, flexible and inexpensive hoses.The wall of these hoses is provided with convolutions or corrugations,which results in added flexibility and crush and kink resistance. Thecorrugated shape makes the hose return to its original shape after beingbent, compressed or stretched. Moreover, the corrugated shape preventsthe hose from collapsing when the pressure inside the hose is reduced.

The corrugated shape of such a hose results in an internal surface withprojections and recesses. It was found that the hose produces anannoying whistle when an air stream passes through its interior,especially at high rates of air flow. The whistle occurs when the hoseis in stretched condition, but particularly when the hose is bent. Thewhistle is caused by resonance of audible harmonics which are createdwhen the air, which is blown or sucked through the hose, strikes thecorrugations of its internal surface.

From U.S. Pat. No. 4,756,045 a flexible hose of a plastic material isknown which is produced by an extrusion blow-moulding process. Theflexible hose disclosed in U.S. Pat. No. 4,756,045 has an internalsurface comprising alternating projections and recesses, recesses of agreater depth and/or width alternating with recesses of a smaller depthand/or width. These alternating corrugations provide the hose with aroughened internal surface which reduces whistle by breaking up the flowof the passing air: the resonance caused by the harmonics created at thelarger recesses is counteracted by the resonance caused by the harmonicscreated at the smaller recesses, which have a different frequency. Thissolution to the problem of unwanted whistle however has the disadvantagethat the rougher internal surface amounts to a higher internal airresistance, giving rise to a loss of air pressure along the corrugationsof the internal surface and thus to a loss of capacity of the hose.

There is thus a need for a flexible corrugated hose with which theproblem of whistle can be solved without however increasing the internalair resistance of the hose. It is the object of this invention toprovide a flexible corrugated hose which shows a reduced internal airresistance.

This is achieved according to the invention with the technical featuresof the characterising part of the first claim.

According to the invention each internal projection of the hose has asubstantially flat and smooth top face. These flat top faces can preventpressure loss on the internal protrusions and give the whole of theinternal surface of the hose a smoother appearance, so that the airresistance of the interior of the hose can be reduced. By limitingpressure loss to the recesses and preventing pressure loss on theprotrusions, the overall pressure loss over the entire length of thehose can be reduced.

As an air stream passes through the interior of the hose and the airstrikes the side walls of the recesses, harmonics are created. Becauseof their substantially flat shape, the top faces form dampers for theharmonics which are created when air strikes the side walls of theinternal recesses of the hose. The result is that a vibration created atone recess can be damped before the air reaches the next recess. Thisdamping effect is supplied by the top face of the projection in betweenthe two successive recesses. This damping effect has the advantage thatless air resistance and less loss of air pressure occurs in the hose ofthe invention compared to the hose described in U.S. Pat. No. 4,756,045in which the harmonics are counteracted by other harmonics of adifferent frequency. The damping effect in the hose of the inventionreduces the amount of air vibrations created in the hose, whereas thecounteracting effect in the hose described in U.S. Pat. No. 4,756,045increases the amount of air vibrations created in the hose and causescomparatively more loss of air pressure.

An advantage of the smoother appearance of the internal surface of thehose is that less dust ends up in the internal recesses of the hose whenit is used as a vacuum cleaner hose.

The ratio between the width of the top faces W1 and the width of therecesses W2 is preferably larger than or equal to 2.2, preferablyW1/W2≧3.5, in order to obtain that the damping effect exerted by the topfaces can last long enough to sufficiently damp a vibration created atone recess before the air reaches the next recess. In this wayinterference of harmonics and a resulting production of whistle can beprevented. The first width W1 is the distance between a firstintersection A of a first tangent line T1 with a second tangent line T2and a second intersection B of a third tangent line T3 with the secondtangent line T2. The second width W2 is the distance between the secondintersection B and a third intersection C of a fourth tangent line T4with a fifth tangent line T5. The first tangent line T1 touches a sidewall of a first recess. The second tangent line T2 touches the top faceof a first projection which is adjacent to the side wall of the firstrecess. The third tangent line T3 touches a first side wall of a secondrecess, this first side wall being adjacent to the first projection. Thefourth tangent line T4 touches the second side wall of the secondrecess, this second side wall opposing the first side wall of thissecond recess. The fifth tangent line T5 touches the top face of asecond projection which is adjacent to the second side wall of thesecond recess.

The inventor has also noted that the hose described in U.S. Pat. No.4,756,045 and other existing hoses of a similar type are onlysubstantially whistle-free at rates of air flow which do not exceed 115m³/h. By providing a hose with a ratio W1/W2≧2.2 according to theinvention, preferably W1/W2≧3.5, a hose is obtained which is stillsubstantially whistle-free at higher rates of air flow, for example at130 m³/h or higher. This is important because the rate of air flow ofvacuum cleaners has risen from 90 m³/h in the past to 130 m³/h nowadays,so that the existing hoses are no longer applicable as they producewhistle at a rate of air flow of 130 m³/h. This feature of the hose ofthe invention can also be advantageous in other industrial applianceswhich involve a flexible hose with an air stream passing through itsinterior.

In order to obtain a hose with recesses which are as narrow as possibleto prevent whistle especially at high flow rates, it is preferred thatthese recesses have substantially straight side walls which extendalmost perpendicular to the longitudinal direction of the hose. Inparticular side walls are preferred of which the tangent line forms anangle of approximately 90 to 100° with the plane formed by top faces ofthe internal projections.

According to another preferred embodiment of the invention the externalsurface of the hose comprises projections and recesses, higherprojections alternating with lower projections and these lower externalprojections corresponding to the substantially flat top faces of theinternal projections. These lower external projections are provided tocollect an excess of plastic material and to prevent that plasticmaterial piles up onto the projections in between two internal recessesof the internal surface of the hose during the moulding process. Inother words, these lower external projections permit the plasticmaterial to take such a shape that the internal projections have asubstantially flat top face.

It is also preferred that along the internal recesses of the hose thewall has a substantially uniform material thickness T. Furthermore it ispreferred that the transition between the top face of each internalprojection and the side wall of each internal recess is formed by asubstantially rounded edge. This rounded edge preferably has a curvaturewith a radius which is smaller than or equal to 1.5 times the materialthickness T. This is preferred because the radius of the curvature ofthe rounded edges has to be small enough in order to prevent that thesubstantially flat area of the top faces of the internal projectionsbecomes too small, which would result in a reduction of the dampingeffect of the top faces and interference of harmonics which are createdwhen a passing air stream strikes the side walls of the internalrecesses, thus producing of whistle.

The hose of the present invention is further preferably provided with ahollow longitudinal protuberance or score, in which for example one ormore electrical conductors, a smaller tube containing conductors andpossibly also a pull relief may be embedded, or which can be used fortransporting a second gas or a fluid.

The present invention also relates to a mould for moulding a flexiblehose as described above. Such a mould has a wall with a corrugatedsurface comprising in longitudinal direction alternating projections andrecesses which extend in radial direction in the mould. The projectionsand recesses correspond to the projections and recesses of the externalsurface of the hose.

The mould is preferably provided with projections and deeper recessesalternating with less deep recesses, the deeper recesses extendingfurther into the wall of the mould. At a given supply rate of the moltenplastic material in the moulding process, the less deep recesses collectan excess of the plastic material urged against the projections of themould, thus permitting the plastic material to form a hose with internalprojections which have a substantially flat top face according to theinvention. The less deep recesses are capable of preventing the plasticmaterial from piling up and forming a hose with internal projectionswhich have a convex shape, which is unwanted as this could result inhose with a higher air resistance along its internal surface, more lossof air pressure over its entire length and a production of whistleduring operation.

The less deep recesses of the mould can have any shape, but in apreferred embodiment of the invention the less deep recesses have asubstantially semicircular shape. The radius of this semicircular shapeis preferably about equal to the material thickness T of the wall of thehose in order to obtain that the internal projections of the hose have asubstantially flat top face, and not a top face which has a convex orconcave shape.

The deeper recesses of the mould have a shape which permits the plasticmaterial to flow easily into them. With this shape a hose of the desiredstrength and flexibility is formed and the removal of the hose after themoulding process is facilitated. To this purpose each of the deeperrecesses of the mould preferably has two opposing side walls which forman angle of approximately 90 to 100° with the longitudinal direction ofthe mould. Furthermore, each of these recesses preferably has a bottomwidth in the wall of the mould of about 2 to 3 and preferably about 2.5times the desired material thickness T of the wall of the hose, in orderto obtain a hose with recesses which are narrow enough to be able toprevent whistle and wide enough to ensure the flexibility of the hose.Also, the bottom corners of these deeper recesses preferably areslightly rounded, which can facilitate the removal of the mould from thehose. The depth of these deeper recesses is preferably about 1.5 timestheir bottom width in order to obtain a hose with sufficient strength.

It is preferred that the mould further has such a shape that the hoseproduced in the moulding process has internal projections with edgeswhich are as little rounded as possible. To this purpose the transitionsbetween the projections protruding from the wall of the mould and theside walls of each of the deeper recesses are preferably formed bysharp, not-rounded edges. The inventor has noted that providing themould with such sharp, not-rounded edges does not adversely affect thestrength of the hose at these edges, in other words does not lower thetear strength of the hose.

In one embodiment the mould has a wall provided with a longitudinalprotuberance or score. In that way a hose can be produced which shows acorresponding hollow longitudinal score or protuberance, in which forexample one or more electrical conductors, a smaller tube containingconductors and possibly also a pull relief may be embedded, or which canbe used for transporting a second gas or a fluid.

The invention is further elucidated by means of the appended figures andthe description of these figures. In the figures below, the samereference numbers always refer to the same parts.

FIG. 1 shows a longitudinal section of a flexible hose with a corrugatedwall according to the invention in a state in which no forces areapplied to the hose.

FIG. 2 shows an enlargement of a part of the corrugated wall of thehose.

FIG. 3 shows a part of a mould for moulding a flexible hose with acorrugated wall according to the invention.

FIGS. 4a and 4 b show cross-sections of hoses in which respectively alongitudinal protuberance and a longitudinal score is provided.

The longitudinal section of the hose 1 shown in FIG. 1 reveals that thehose 1 has a corrugated wall 2 with an internal surface 3 whichcomprises projections 4, 5 alternating with recesses 6, 7, and anexternal surface 16 which comprises projections 23, 24 alternating withrecesses 19, 20.

The hose 1 may be made by moulding a plastic material, for instance athermoplastic or a thermosetting material. Suitable thermoplasticsinclude polyethylene, polypropylene, copolymers thereof and any otherthermoplastic material known to the person skilled in the art.

The corrugations of the wall of the hose may have a circular, helical,oval, square or any other shape known to the person skilled in the art.

Each internal projection 4, 5 shows a substantially flat and smooth topface 8, 9. The substantially flat top faces 8, 9 give the internalsurface 3 of the hose 1 a smoother appearance, which can result in alower air resistance, less loss of air pressure and a reduction ofwhistle. This is because the substantially flat and smooth top facesform dampers for the harmonics which are created by passing air at therecesses.

Each internal recess 6, 7 comprises two opposing side walls 10, 11, 12,13. The top face 8, 9 has a first width W1 and the recess 6, 7 has asecond width W2. The first width W1 is the distance between a firstintersection A of a first tangent line T1 with a second tangent line T2and a second intersection B of a third tangent line T3 with the secondtangent line T2. The second width W2 is the distance between the secondintersection B and a third intersection C of a fourth tangent line T4with a fifth tangent line T5. The first tangent line T1 touches a sidewall 11 of a first recess 6. The second tangent line T2 touches the topface 8 of a first projection 4 which is adjacent to the side wall 11 ofthe first recess 6. The third tangent line T3 touches a first side wall12 of a second recess 7, this first side wall 12 being adjacent to thefirst projection 4. The fourth tangent line T4 touches the second sidewall 13 of the second recess 7, this second side wall 13 opposing thefirst side wall 12 of this second recess 7. The fifth tangent line T5touches the top face 9 of a second projection 5 which is adjacent to thesecond side wall 13 of the second recess 7. When the ratio W1/W2 ischosen larger than or equal to 2.2 according to the invention andpreferably larger than or equal to 3.5, the top faces 8, 9 are largeenough to be capable of damping a harmonic, which is created by passingair at one recess 6, before it reaches the next recess 7. In this way,interference of harmonics which are created at successive recesses canbe prevented, so that no whistle occurs when an air stream passesthrough the hose.

In order to obtain recesses 6, 7 which are as narrow as possible andthus prevent whistle, the tangent lines T1, T3, T4 of the side walls 11,12, 13 of the recesses 6, 7 form an angle α of approximately 90 to 100°with the tangent lines T2, T5 of the top faces 8, 9 of the internalprojections 4, 5. This angle α is preferably about 93 to 94°.

Along the internal recesses 6, 7 of the hose 1 the wall 2 preferably hasa substantially uniform material thickness T. The transition between thetop face 8, 9 of each internal projection 4, 5 and the side wall 10, 11,12 ,13 of each internal recess 6, 7 is formed by a substantially roundededge 14, 15, which results naturally from the moulding process, as themolten plastic material which is urged against the sharp edges 31, 32 ofthe mould 21 naturally takes a rounded shape on these edges. The roundededge 14, 15 preferably has a curvature with a radius R1 which is smallerthan or equal to 1.5 times the material thickness T of the wall 2 of thehose 1. By keeping the radius R1 of the curvature of this rounded edge14, 15 as small as possible, the overall smoother appearance of theinternal surface 3 of the hose 1 is ensured. The result is that the lossof air pressure during operation of the hose can be reduced and theproduction of whistle can be prevented.

As shown in FIG. 2 the hose 1 comprises an external surface 16 withprojections 17, 18 and recesses 19, 20, preferably higher projections 18alternating with lower projections 17 and these lower externalprojections 17 corresponding to the substantially flat top faces 8, 9 ofthe internal projections 4, 5. These lower external projections 17 mayhave a substantially semicircular shape with a radius R2 which is aboutequal to the material thickness T of the wall 2 of the hose 1. Theselower external projections 17 are provided to collect an excess ofplastic material and to prevent that plastic material piles up onto theprojections between two successive deeper recesses 25 of the mouldduring the moulding process. In other words, these lower externalprojections 17 permit the plastic material to take such a shape that theinternal projections 4, 5 of the hose 1 have a substantially flat topface 8, 9 and not a top face with a convex or concave shape.

The hose 1 may also be provided with a hollow score 34 or protuberance33 in longitudinal direction which has a smaller diameter an he diameterof the hose 1. In this longitudinal score 34 or protuberance 33 forexample one or more electrical conductors, a smaller tube containingconductors and possibly also a pull relief may be embedded. It may alsobe used for transporting a second gas or a fluid. This score 34 orprotuberance 33 is provided in a moulding process by using a specialmould which has a longitudinal protuberance or score. After this processone or more electrical conductors, a smaller tube containing conductorsand possibly also a pull relief may be embedded in the protuberance 33or score 34 of the hose 1, or it can be left empty in case it will beused for transporting a second gas or a fluid. The protuberance 33 orscore 34 of the hose 1 can finally be closed by welding together thelongitudinal edges of the hose 1, which form the transitions between thescore or protuberance and the hose itself.

The mould 21 shown in FIG. 3 comprises a surface 22 with in longitudinaldirection projections 23, 24 and recesses 25, 26, deeper recesses 25alternating with less deep recesses 26. The deeper recesses 25 extendfurther into the surface 22 of the mould 21.

Suitable moulding processes for producing a flexible hose includeblow-moulding processes, vacuum-moulding processes or any other mouldingprocess known to the person skilled in the art. In a blow-mouldingprocess molten plastic material is extruded in the interior of themould, and then blown onto its internal surface by applying pressurisedair to the centre of the plastic material. In the case of avacuum-moulding process the mould is provided with narrow gaps whichextend circumferentially and are a few tenths of a millimeter wide.Through these gaps a vacuum which is created around the outside of themould is applied to the plastic material which is extruded inside themould, so that the plastic material is sucked onto the internal surfaceof the mould. In comparison with blow-moulding, vacuum-moulding showsthe advantage that a higher production speed can be obtained, in someconditions, as the vacuum applied to the outside of the mould at thesame time helps for providing a longer cooling contact. However,vacuum-moulding shows the disadvantage that the narrow gaps in the mouldlead to irregularities on the external surface of the hose.

A blow-moulding process using the mould 21 can be described as follows.Molten plastic material is supplied to an extruder, from which themolten plastic material is introduced between two rotating mould chains.The mould chains face each other and rotate in opposite direction inrelation to each other. Each mould chain comprises several separatemoulds with a length of about 6 cm and a semicylindrical score inlongitudinal direction of the mould chain in which the corrugatedsurface is provided. On one side these two mould chains come together,pressing the separate moulds together in such a way that a mould of onemould chain is pressed against a mould of the second mould chain, thetwo moulds having an opposite semicylindrical score, so that a cavity isformed with the desired cylindrical, longitudinally corrugated shape.The molten plastic material is introduced in the mould at the pointwhere the two mould chains come together. Pressurised air is blownthrough the centre of the cylinder of plastic material, so that itexpands and is urged against the corrugated wall of the mould, theplastic material thereby flowing into the deeper and the less deeprecesses and onto the projections of the mould, forming the hose 1.Thus, it can be seen that the projections 23, 24 of the mould 21correspond to the recesses 19, 20 of the external surface 16 of the hose1, that the deeper recesses 25 of the mould 21 correspond to the higherexternal projections 18 of the external surface 16 of the hose 1, andthat the less deep recesses 26 of the mould 21 correspond to the lowerexternal projections 17 of the external surface 16 of the hose 1. Theless deep recesses of the mould here function as collectors for anexcess of plastic material, so that the plastic material is shaped suchthat the internal projections of the formed hose have a substantiallyflat top face. Because of the rotation of the mould chains the hose ispulled away from the extruder along with the separate moulds of the twomould chains. The extrusion speed of the cylinder of plastic material isadapted to the linear speed of the mould chains in accordance with therequired wall thickness T for the hose. Before the mould chains reachthe point where their separate moulds come apart, the individual mouldsare cooled down, so that the plastic material solidifies. Finally therotating mould chains separate and the separate moulds are removed fromthe hose.

The width and depth of the less deep recesses 26 of the mould 21 areadapted to the desired material thickness T of the wall 2 of the hose 1,in other words aimed at the amount of plastic material which has to becollected in them to give the internal projections 4, 5 of the hose 1the desired substantially flat top face 8, 9. Thus, the width and depthof the less deep recesses of the mould depends on the extrusion rate ofthe plastic material.

The less deep recesses 26 of the mould 21 preferably have a semicircularshape with a radius R3 which is about equal to the material thickness Tof the hose 1. This radius R3 of the less deep recesses 26 of the mould21 substantially equals the radius R2 of the lower external projections17 of the hose 1.

It is also preferred that each deeper recess 25 of the mould 21 has twoopposing side walls 27, 28 which form an angle β of 90 to 100°,preferably 93 to 94° with the longitudinal direction of the mould 21.Furthermore, each of these deeper recesses 25 preferably has a bottomwidth W3, measured at the bottom of the deeper recesses 25 in the wallof the mould 21, of about 2.5 times the desired material thickness T ofthe wall 2 of the hose 1. Also, the bottom corners 29, 30 of thesedeeper recesses preferably are slightly rounded. The depth D3 of thesedeeper recesses 25 is preferably about 1.5 times their bottom width W3.By providing the deeper recesses 25 of the mould 21 with thesecharacteristics, the plastic material can easily flow into them in themoulding process, forming a hose 1 of the desired strength andflexibility. These characteristics of the deeper recesses 25 of themould 21 also facilitate the removal of the mould 21 from the hose.

It is further preferred that the transition between each projection 23,24 and the side wall 27, 28 of each of the deeper recesses 25 is formedby a sharp, not-rounded edge 31, 32. This has the advantage that thehose 1 produced in the moulding process has internal projections 4, 5with edges 14, 15 which may be rounded but preferably as little aspossible, which is wanted to possibly reduce whistle.

REFERENCE LIST

1 hose

2 wall

3 internal surface

4, 5 internal projection

6, 7 internal recess

8, 9 top face

10, 11 side wall

12, 13 side wall

14, 15 rounded edge

16 external surface

17 lower external projection

18 higher external projection

19, 20 external recess

21 mould

22 surface

23, 24 projection

25 deeper recess

26 less deep recess

27, 28 side wall

29, 30 bottom corners

31, 32 sharp, not-rounded edge

33 protuberance

34 score

W1 width of top face

W2 width of recess

W3 bottom width of deeper recess

D3 depth of deeper recess

A, B, C intersection

T1, T3, T5 tangent line of side wall

T2, T4 tangent line of top face

αangle between T1, T3, T4 and T2, T5

βangle between side wall and longitudinal direction of the mould

T material thickness

R1 radius of rounded edge

R2 radius of lower external projection

R3 radius of less deep recess

What is claimed is:
 1. A flexible hose comprising: a corrugated wall(2), including an internal surface (3) with projections (4, 5) andrecesses (6, 7), said hose (1) being obtained by moulding a plasticmaterial, each internal projection (4, 5) comprising a substantiallyflat and smooth top face (8, 9), wherein each internal recess (6, 7)includes two opposing side walls (10, 11, 12, 13), said top face (8, 9)having a first width (W1) and said recess (6, 7) having a second width(W2), the ratio between first width and second width (W1/W2) beinglarger than or equal to 2.2, the first width (W1) being the distancebetween a first intersection (A) of a first tangent line (T1) with asecond tangent line (T2) and a second intersection (B) of a thirdtangent line (T3) with the second tangent line (T2), the second width(W2) being the distance between the second intersection (B) and a thirdintersection (C) of a fourth tangent line (T4) with a fifth tangent line(T5), the first tangent line (T1) touching a side wall (11) of a firstrecess (6), the second tangent line (T2) touching the top face (8) of afirst projection (4) adjacent to said side wall (11) of the first recess(6), the third tangent line (T3) touching a first side wall (12) of asecond recess (7), said first side wall (12) being adjacent to a first(4) of said projections (4), the fourth tangent line (T4) touching thesecond side wall (13) of the second recess (7), said second side wall(13) opposing the first side wall (12) of said second recess (7), andthe fifth tangent line (T5) touching the top face (9) of a secondprojection (5) which is adjacent to the second side wall (13) of thesecond recess (7).
 2. A flexible hose according to claim 1, wherein thetangent line (T1, T3, T4) of the side wall (10, 11, 12, 13) of eachinternal recess (6, 7) forms an angle (α) of approximately 90 to 100°with the tangent line (T2, T5) of the top face (8, 9) of each internalprojection (4, 5).
 3. A flexible hose according to claim 1 characterizedin that wherein the hose (1) comprises an external surface (16) withrecesses (19, 20) and projections (17, 18) higher projections (18)alternating with lower external projections (17) and said lower externalprojections (17, 18) higher projections (17) corresponding to thesubstantially flat top faces (8, 9) of the internal projections (4, 5).4. A flexible hose according to claim 1, wherein along the internalrecesses (6, 7) of the hose (1) the wall (2) has a substantially uniformmaterial thickness (T) and a transition between the top face, (8, 9) ofeach internal projection (4, 5) and the side wall (10, 11, 12, 13) ofeach internal recess (6, 7) is formed by a substantially rounded edgae(14, 15).
 5. A flexible hose according to claim 4, wherein the roundededgae (14, 15) has a curvature with a radius (R1) which is smaller thanor equal to 1.5 times the material thickness (T).
 6. A flexible hoseaccording to claim 1 wherein the hose (1) comprises a hollowlongitudinal protuberance (33) or score (34).